SUFFOLK, Va. (WAVY) – Carbon monoxide was detected at a Wal-Mart in Suffolk Tuesday, making it the second time it six months the store has had a reading.

Diana Klink with the City of Suffolk said an employee of the store on North Main Street called to report an odor of gas in the store around 9:35 a.m.

Using gas meters, fire and rescue crews detected carbon monoxide in the store. The store was evacuated around 9:45 a.m. and reopened by 1:15 p.m. No injuries were reported.

Klink said Virginia Natural Gas was dispatched to the scene and police were working with traffic control while the store was closed. The cause of the odors couldn’t be isolated right away because the HVAC units are remotely controlled at a facility out of state.

The problem was later found to be with a rooftop HVAC system.

This is the second time carbon monoxide has been detected at that same store. In October, crews responded to the store for reports of a strong smell of gas and detected carbon monoxide using gas meters. A leak was found by Virginia Natural Gas.